The locks used in general briefcases or luggage cases can be classified into combination locks and noncombination locks i.e. locks which must be opened by the right key. The keys for a specific type of lock are all the same. Therefore, it can often be seen that the key for the lock of a specific briefcase can be used to open that of another briefcase. Consequently, many persons pay no attention to the preservation of the keys. The noncombination locks thus provide more ornamentation than inaccessibility. However, sometimes it is still necessary to lock a case for safety purposes. This often incurs trouble to find the key. Many cases, therefore, are provided with a combination lock to save the trouble in the preservation of the keys.
General combination locks for cases are combination-changeable. This means that after buying a case, the user may select a preferred combination for opening the lock thereof. This provides much convenience and utility and is the reason why the cases with a combination lock are widely used. Nevertheless, the combination locks with horizontal dials for cases have two main disadvantages: (A) their thickness is much larger than (e.g, about twice) that of a noncombination lock (the combination locks with vertical dials are even larger in thickness and therefore are preferably used in luggage cases) and thus are not suitable to be used in briefcases, and (B) their combination cannot be changed easily (i.e. in combination changing operations of the locks for current cases, a large force must be exerted to rotate the combination dials; this causes inconvenience and is unacceptable for ladies having weak muscles and slender fingers).
A combination lock is combination-changeable by having its dial engaged with or disengaged from the corresponding driven wheel. In normal use, the dial is engaged with the wheel; when the combination is to be changed, the dial and wheel are disengaged from each other so that the relative position thereof can be changed to achieve the effect of changing the combination. The combination dials of the locks are all arranged coaxially, i.e, the combination dials and the corresponding driven wheels are rotated on the same axial. To change the relative position (for combination changing purposes) between a dial and the corresponding driven wheel, they must be completely disengaged from each other. There must be sufficient space in the lock for accommodating the thickness of every combination dial and the corresponding driven wheel and for them to be disengaged from each other. Therefore, the thickness of this type of locks must be much larger than that for a noncombination lock. Moreover, since each combination dial and the corresponding driven wheel are retained to engage with each other by a spring force, a large force must be exerted to rotate the combination dial for changing the relative position between the dial and wheel when the combination is to be changed.